The present invention relates to a packet data communication system with a ring type transmission line represented by a local area network (LAN) and, more particularly, to a high speed, large capacity packet data communication system for efficiently transmitting various data such as multiplexed voice, moving images and burst data, etc.
Advancement of hardware/software in the field of information processing field is notable in recent years. With improvement in the processing capability of computers and microprocessors, high performance and spreading of communication terminals and work stations, large capacity files such as optical disk and distribution of processing with development of distributed databases, a network is established between these types of hardware and the amount of data handled by such networks is increasing.
In addition, improvements in function of image processing hardware/software and the advent of TV conference systems requires a network which can handle unified high speed and large capacity image information in addition to the existing voice and data.
FIG. 1 is an example of structure of the said network (local area network). As the trunk network, a ring type transmission line 1 is employed. In the course of the ring type transmission line 1, a plurality of interface nodes 2 are provided and each interface node accommodates various systems. Namely, this is a bus-type local area network for communication between a plurality of workstations 5, digital PABX 6, telephone sets and facsimiles connected and controlled by the digital PABX 6, remote unit 7 which accommodates data terminals, low speed ring type local area network 8, communication control apparatus 11 of main frame computer 12 and adapter 10 which accommodates its TSS terminals, TV conference system 13 and composite multiplexing apparatus 9 for connection with a high speed leased digital line. Each system is respectively connected to the high speed ring type network 1 through an interface node 2 and the system-to-system communication can be made through the control of such interface node 2. In addition, the high speed ring type network 1 is supervised by the supervisor node 3. As an access method to such ring type network 1, a slot ring system is proposed. In this slot ring system, a plurality of fixed length slots are circulating on the network 1, each interface node 2 detects an available slot, the data from the terminal(s) accommodated by that node 2 is loaded to the detected available slot after it is converted to packet data and then such packet data is sent to the other interface nodes 2.
As a method of realizing a high speed and large capacity network, it is possible to increase the transmission rate of each packet or to transmit in parallel a plurality of packets without changing the transmission rate of packets. High speed operation of LANs has been realized almost by the former method because it is estimated that the number of gates of control circuits increases if the latter method is employed. Accordingly, little investigation has been made into the latter method.
However, when considering realization of LAN having a transmission capacity in the order of several hundred Mb/s, problems for realization, such as high power consumption of ECL circuits and "difficulty in handling" during debug/maintenance, are generated in the method of increasing the transmission rate of each packet. As an effective method for avoiding such problems, consideration is given to employ the parallel communication system where high speed and large capacity transmission is realized by transmitting in parallel a plurality of packets and each packet is processed by a low speed TTL circuit.